Means for controlling the capacity of compressors



May 10, 1960 N. E. B. LARSSON ETAL 2,936,106

MEANS FOR CONTROLLING THE CAPACITY OF COMPRESSORS Filed March 21, 1955 2 Sheets-Sheet 1 May 10, 1960 N. E. B. LARSSON ET AL 2,936,106

MEANS FOR CONTROLLING THE CAPACITY OF COMPRESSORS Filed March 21, 1955 2 Sheets-Sheet 2 MMA W Jp'wZi/n/ United States Patent MEANS FOR CONTRGLLING THE CAPACITY OF COMPRESSORS Nils Erik Birger Larsson and Torsten Loberg, Finspong, Sweden Application March 21, 1955, Serial No. 495,499

Claims priority, application France April 14, 1954 8 Claims. (Cl. 230-30) In certain compressor refrigerating systems great demands are made upon the maintenance of a constant evaporation temperature or an evaporation temperature which only varies within very narrow limits. It is already known to obtain this effect Without changing the speed of the compressor by controlling the capacity of the compressor. An already known method for carrying out such a control is to open the suction valves of the compressor by positive acting means. Such means may, for instance, comprise a claw-shaped member provided within the suction chamber of the compressor the claws of which extend through the suction channels provided between the suction chamber and the cylinder chamber of the compressor for removing the suction valves from the seats engaged thereby which are provided at the ends of the suction channels facing the cylinder chamber. Such claw-shaped valve depressors are controlled, as a rule, by means of a control piston, and in such cases in which said piston may assume an intermediate position between its end positions, corresponding to closed and fully opened suction valves, respectively, the suction valves operate by frequently repeated rapid strokes against the valve depressors, whereby damages may be caused on the suction valves and the valve depressors as well.

In such a controlling system the operating medium will, as a result, flow back and forth between the suction chamber and the compressor cylinder, which gives rise to a loss of power resulting in an increase of temperature of the operating medium provided said medium is contained in a closed system. A further drawback is that by this means no continuous capacity control may be obtained. 1

The object of the present invention-is to provide a capacity control for refrigeration compressors while avoiding the drawbacks above referred to. To this end the control is carried out according to the invention in such a way that the opening of the suction valves is preceded by a closing of the connecting channels between the suction chamber and the cylinder chamber by means of a separate valve, and is followed by an evacuation of operating medium remaining in the compressor cylinder, said medium being passed to the suction chamber by way of a non-return valve. By this means the suction valves are prevented from vibrating against the valve depressors, a furflaer result being that the compressor will operate in a completely unloaded state and with the smallest consumption of power possible due to the evacuated state of the cylinder.

The means for carrying out the capacity control according to the invention is characterized, chiefly, by the fact that the valve depressors are combined with a cylinder valve provided in the suction chamber which cooperates with seats at the ends of the connecting or suction channels facing the suction chamber in order to interrupt the communication between the suction chamber and the compressor cylinder independently of the suction valves, said cylinder valve being allowed to effect a movement suificient to cause the valve depressors to open the suction valves while maintaining the interruption of the communication between the suction chamber and the cylinder of the compressor at the ends of the suction channels facing the suction chamber.

A further feature of the invention involves that the closing valve is provided with one or more passages controlled by a non-return valve in order to enable the evacuation of operating medium from the compressor cylinder to the suction chamber in the closed state of the closing valve.

A further feature of the invention resides in constructing the cylinder valve as a movable cylinder in cooperation with a stationary piston or as a movable piston operating in a stationary cylinder, said cylinder and said piston constituting a piston motor operating under the action of a pressure medium admitted from a controlling device provided remote from the compressor.

In the accompanying drawings two embodiments of the invention are shown. Figs. 1 and 2 are sections taken in the longitudinal direction of the compressor through the suction chamber thereof, a device according to the first embodiment of the invention being provided in said chamber, said device being likewise shown in section. Figs. 3 and 4 are similar sections of the suction chamber of a compressor in which a device according to the second embodiment of the invention is provided. In Figs. 1 and 3 the suction valve is shown in closed position, and the closing valve provided in the suction cham-- ber is shown in open state, while in Figs. 2 and 4 the suction valve is open and the closing valve is closed. In Figs. 1 and 3 the valve depressors are removed from the range of movement of the suction valve, while in Figs. 2 and 4 the valve depressors keep the suction valve in its completely open position.

With reference to the drawing, the reference numeral 1 indicates the cylinder of a compressor having a cylinder chamber 40, a reciprocable piston 4 located in said chamber and a cover 2, a plate 3 forming a wall between the suction chamber 5 formed in the cover 2 and the cylinder chamber. The reference numeral 6 indicates the suction valves, and 7 indicates the suction or connecting channels between the suction chamber 5 and the cylinder chamber. The suction valve 6 comprises in both embodiments of the invention a spring-loaded annular plate which cooperates with seats at the lower ends of the suctionchannels 7 facing the cylinder chamber.

The capacity control device according to the invention comprises in both embodiments as its main element a cylinder valve 8 provided in the suction chamber 5 for cooperation with seats formed at the upper ends of the suction channels 7 facing the suction chamber. Said cylinder valve 8 consists, in both embodiments shown, of a cylinder which is slidably mounted on a piston 9 secured to the intermediate wall 3, the axis of said piston and cylinder being in the cases under consideration parallel with the direction of movement of the compressor piston. The cylinder valve carries the suction valve depressors or openers 1i). Said depressors comprise in each of the embodiments shown a set of pins parallel with the axis of the piston and cylinder which are positioned at equal distances apart along a circle the radius of which is equal to the average radius of the annular suction valve 6. The pins 10 which constitute the suction valve depressors extend each through a separate one of the suction channels 7. Placed upon a shoulder formed on the cylinder valve 8 is an annular plate 11 which is biased by a spring 12 tending to force the plate against said shoulder by acting on the inner peripheral portion of the plate 11. The outer peripheral portion of plate 11 covers one or more passages 13 formed in the cylindrical wall of cylinder valve 8, said passages extending from the lower or operating surface of cylinder valve 8 to the shoulder supporting the valve plate 11. Said valve plate is comparatively thin and capable of bending along its periphery upwardly into a sort of cup under the action of the pressure from medium in the passage or passages 13 so as to uncover the upper ends of said passages, as will be hereinafter more clearly described. The passages 13 are situated in axial alignment with one or more of the suction channels 7.

Between the cylinder-shaped valve 8 and the stationary piston 9 on which the cylinder valve 8 may slide a space 14 is formed, to which a connection is established through openings 15 in a hub-shaped portion of the piston 9 to a control pipe 16 which extends to the outside of the suction chamber through a packing, not shown, in the cylinder cover 2, said control pipe being connected outside the compressor to a control device, not shown, of such an arrangement as to start when the compressor draws more operating medium from the suction chamber 5 than required or when the compressor draws a smaller quantity of operating medium from the suction chamber than that required, and restore the proper operation of the compressor by changing the pressure inside the space 14. Any desired medium may be used for transmitting the pressure to the space 14, as for instance, oil under pressure.

In the embodiment shown in Figs. 1 and 2, the top surface of plate 3 is formed with a circular depression 17, as by a turning action, said depression being concentric with the axis of piston 9 and cylinder valve 8 and having a diameter corresponding to the diameter of the lower portion of the cylinder valve 8 so as to be capable of receiving the lower end thereof. The depth of the depression 17 is slightly greater than the opening stroke of the suction valve. 8 The valve openers it are of such a length as to reach the valve plate 6 only at that moment at which the cylinder valve 8 reaches the level of the upper surface of plate 3 by its lower end, thereby covering the depression 17 and interrupting the connection between the suction chamber 5 and the suction channels 7. During the continued movement of the cylinder valve 8 down to the bottom of the depression 17 the suction valve 6 is opened without permitting any medium to pass from the suction chamber 5 to the cylinder chamber because of the covering of the depression 17 by the cylinder valve 8.

In the embodiment shown in Figs. 3 and 4 the intermediate plate 3 has no depression like 17 of Figs. 1 and 2. In this case the cylinder valve 8 carries a ring 18 slidably mounted on the cylindrical peripheral surface of cylinder valve 8 so as to be capable of moving thereon from a lower position in which its lower end projects below the under surface of cylinder valve 8 by an amount slightly greater than the opening stroke of the suction valve 6,

to an upper position in which the lower edge of ring 18 is on a level with the lower surface of cylinder valve 8. For limiting the movement of ring 18 with relation to cylinder valve 8 the ring' is formed with an inwardly projecting flange engaging the space between a shoulder formed on the cylinder valve 8 for determining the lowermost position of ring 18 with relation to cylinder valve 8 and a flange 19 comprising a ring rigidly secured to the cylinder valve 8 for determining the uppermost position of ring 18 with relation 'to cylinder valve 8.

The operation of the embodiments described is substantially as follows:

When one cylinder of a multi-cylinder compressor is under full load, the respective cylinder valve 8 is in its upper position in which it is held by the action of the pressure medium in space 14 Provided the compressor would draw in a large quantity of operating medium for the suction chamber 5 than that necessary for satisfying the requirements, the control device for the pressure medium in the control pipe 16 starts operation andre-n duces the pressure of said medium. As -a result, the spring 12 may press the cylinder valve 8 downwards, causing the valve to effect a gradual throttling of the admission of operating medium from the suction chambet 5 via the suction channels 7 to the compressor cylinder. The cylinder valve 8 may at this operation remain in a position of equilibrium between its end positions, provided the suction of operating medium to the cylinder reaches the value required before the cylinder valve 8 has reached its lowermost position. If, on the other hand, the suction is so powerful as to render an unloading of the cylinder desirable, the throttling action continues by the cylinder valve 8 moving further downwards until, in the embodiment of Figs. 1 and 2, cylinder valve 8 reaches the upper edge of the depression 17 or until, in the embodiment of Figs. 3 and 4, the ring 18 is brought into contact with the upper surface of the intermediate plate 3 by its lower edge. The admission of operating medium from the suction chamber 5 to the cylinder is cut off at the upper ends of the suction channels 7 by this moment. In this position of the cylinder valve 8 the suction valve depressors 16 of both embodiments have reached the top surface of suction valve 6. During the continued downward movement of the cylinder valve 8 the suction valve depressors will thus force the suction valve 6 downward, thereby opening a connection between the cylinder chamber and the suction channels 7. The operating medium remaining in the cylinder chamber may then escape during the upward stroke of the compressor piston through the channels 7 and the passages 13 in communication therewith and pass into the suction chamber 5 by lifting the outer portion of valve plate 11 which acts in conjunction with spring 12 as a non-return valve for the passage or passages 13.

Due to the fact that the admission of operating medium from the suction chamber to the cylinder chamber is cut off by the actuation of cylinder valve 8, and the operating medium remaining in the cylinder chamber is allowed to escape therefrom to pass into the suction chamber, the continued opening of the suction valve is facilitated and damage of the plate 6 of suction valve is avoided, since the plate 6 is held pressed against the depressors 10 without any possibility of moving. When the cylinder valve 8 reaches its lowermost position, that is to say, when in the embodiment of Figs. 1 and 2 cylinder valve 8 reach the bottom of the depression 17 or when in the embodiment of Figs. 3 and 4 the ring 18 is pushed to its uppermost position with relation to cylinder valve 8 when the bottom surface of cylinder valve 8 has reached the top surface of the plate 3, the suction valve 6 is completely opened, as shown in Figs. 2 and 4. By that time the cylinder is evacuated and the compressor works without load and thus with the smallest power consumption possible.

If, on the other hand, the compressor draws in too small an amount of operating medium from the suction chamber as compared with that required, then the control device for the pressure medium in control pipe 16 is caused to act in the reverse manner as before, that is to say, with a view to decreasing the pressure in space 14. Starting from the assumption that the compressor cylinder is evacuated, as supposed in Figs. 2 and 4, and should be put under load, the cylinder valve 8 will be displaced upwards from its lowermost position, in which it has kept the suction valve completely open. During the resulting upward movement of the suction valve towards the seat at the lower ends of the suction channels 7 the admission of operating medium from the suction chamber 5 to the channels 7 is held interrupted, until, in the embodiment of Figs. 1 and 2, cylinder valve 8 and, in the embodiment of Figs. 3 and 4, ring 18 is removed from the top surface of the intermediate plate 3. At the same time the suction valve depressors 10 are lifted out of engagement with the suction valve 6, thereby allowing the cylinder to be loaded 'withoutanyrisk of damaging thesuction valvedue to the valve vibrating against the depressors, since the latter are located above the range or" movement of the suction valve. The cylinder valve 8 will then assume the position Corresponding to the capacity under consideration.

When the compressor is to be started from its position of rest, the pressure of the medium in the control pipe '16 and the space 14 is equal to nought and the cylinder valve 8 is, as a result, in its lower end position, as shown in Figs. 2 and 4. To begin with the medium contained in the cylinder is discharged to the suction chamber 5 by way of the passages 7 and 13 and the non-return valve 11, so that the compressor may accelerate without load. The pressure inside the control pipe 16 increases according as the load increases, the continued control operation being equal to that hereinbefore described.

We claim:

5. 'In a compressoras claimed in claim 4, and in which the valve lifting means of the cylinder valve are of such a length that they engage the suction valve at that moment at which the cylinder valve reaches the top edge of said circular recess, thereby interrupting the connection between the suction chamber and the suction channels before opening the suction valve.

6. In a compressor of the class specified in combina- 1. In a compressor having a cylinder chamber and a I suction chamber, apartition wall separating said chambers from each other, said wall having suction channels extending therethrough providing communication between said chambers, a suction valve provided in the cylinder chamber controlling the cylinder chamber ends of said channels, a cylinder valve provided in the suction chamber for controlling the suction chamber ends of said channels, means carried by said cylinder valve movable freely through said channels from the suction chamber ends thereof for positively lifting the suction valve subsequent to the closing of the suction chamber ends of the channels by the cylinder valve, and a non-return valve provided in combination with said cylinder valve for allowing working fluid remaining under pressure in the cylinder cham her after the closure of the channels by the cylinder valve to escape to the suction chamber.

2. In a compressor as claimed in claim 1, and in which said suction valve lifting means comprises pins fastened to the under surface of the cylinder valve in register with top end of said cylinder, a cylinder top on said wall enclosing a suction chamber, said wall forming a partition between said chambers and having a completely fiat surface towards the suction chamber, a set of channels formed in said wall for connecting the cylinder chamber and the suction chamber with each other, a suction valve seating on said partition wall for controlling the connection betweenthe cylinder chamber and said channels,

a cylinder valve provided in the suction. chamber .con-

trolling the connection between the suction chamber and the suction channels formed in the partition wall between the cylinder and suction chambers, for performing their lifting operation during the last portion of the closin stroke of the cylinder valve. 7

3. In a compressor as claimed in claim 2, and in which the cylinder valve is formed with a passage extending from the lower to the upper surface thereof on a line with one of the suction channels formed in the partition wall between thecylinder and suction chambers, the upper end of said passage being controlled by said non-return valve operable by the pressure in said connection channel.

4. In a compressor as claimed in claim 3, and in which the cylinder valve is formed with a circular operating surface, and the partition wall provided between the cylinder chamber and the suction chamber is formed on its surface facing the suction chamber with a circular recess concentric with said circular operating surface of the cylsaid channels, pins secured to said cylinder valve positively opening the suction valve during the last portion of the closing movement of the cylinder valve, said cylinder valve being located inside the suction chamber and being formed with a ring surrounding the external cylindrical surface of the cylinder valve, said ring being mounted shiftably relative to the cylinder valve in the di-' rection of movement thereof, the stroke of shift being.

slightly larger than the opening stroke of the suction valve for allowing the cylinder valve to cover the connecting channels in the partition wall prior to opening the suction valve.

7. In a compressor as claimed in claim 6, and in which the cylinder valve comprises a movable cylinder mounted on a stationary piston, said movable cylinder and piston being formed with a space therebetween in communication with a controlling conduit connected with said space to admit to said space a control fluid of a pressure determined by an external control mechanism.

8. In a compressor as claimed in claim 7, and in which a non-return valve is positioned on the cylinder valve and comprises an annular flat valve covering the mouth of the return channels formed in said cylinder valve.

References Cited the file of this patent UNITED STATES PATENTS Germany Ian. 8, 1953 

